Cupola treatment of metals



I H, 'KOPPERS. CUPOLA mmmam 0F METALS. APPLICATION FILED SEPT- 3, 1920,1 357;78Q r Patented Nov. 2, 1920.-

2 SHEETS-SHEET l.

H. KOPP ERS.

CUPOLA-TREATMENT 0F METALS;

APPLICATIQN FILED SEPT. 3. 1920,

1,357,780. PatentfldNov- 2,1920.

21 SHEETS-SHEET '2;

ilNITED STATE-S PATENT OFFICE.

HEINRICH KOPPERS, OF ESSEN-ON-THE-RUHB, GERMANY. ASSIGNOR TO THE KOPPERSDEVELOPMENT CORPORATION, A CORPORATION OF PENNSYL- VANIA.

CUPOLA TREATMENT OF METALS.

Specification of Letters Patent.

Patented Nov. 2, 1920.

Application filed September 3, 1920. Serial No. 408,080.

1/ u all w/LOIIL it may concern:

lie it known that I, HEINRICH KorPEns, (assignor to The KoppersDevelopment Corporation, of Pennsylvania,') a citizen of Germany,residing in Essen-on-the-Ruhr, Germany, have invented a new and usefulImprovement in Cupola Treatment of Metals, of which the following is aspecification.

This-invention ,relates to the treatment of metals, such as iron and itsalloys, in cupola furnaces and has for one of its objects to effectetlicient desulfurization of the metal and to obtain a high gradeproduct containing a minimum proportion of sulfur.

The presence of sulfur, especially in iron and its alloys, greatlyimpairs the quality of the metal, when occurring in other than extremelysmall proportions. \Vhen present in iron, sulfur makes the iron muchmore liable to rust; in fact the tendency of iron to deteriorate whenexposed to atmospheric conditions is augmented by the presence ofsulfur, which constitutes an important factor in promoting suchdeterioration. 1n the case of steel, the presence of sulfur not onlymakes the Steel liable to rust, but imparts a brittle quality to thesteel making it diflicult to shape and impairing its strength.Consequently, it is of great importance in the metallurgical industriesto restrict the quantity of sulfur in such metals as iron and steel tomore traces. This invention provides a novel and improved treatment ofthe metal in a cnpola. or remeltiug furnace, by which treatment thesulfur contained in the product of the furnace is limited to meretraces, which do not of the nature of those derived from the iron,

and in rejuvenating the iron with the elements recovered from suchcompounds.

The invention has for other objects such other improvements or:ulvantages in operation and su h other advantageous results as 1na v efound to obtain in the improved processes and apparatus hereinafterdescribed as illustrative examples.

In the accompanying drawings, forming a part of this specification, andshowing, for purposes of exemplification, a preferred manner in whichthe invention may be embodied and practised, but without limiting theclaimed invention specifically to such illustrative instance orinstances Figure 1 is a vertical sectional elevation of a diagrammaticrepresentation of a cupola furnace for practising the improvements ofthe invention;

Fig. 2 is a vertical section on the line 22 of Fig. 1;

Fig. 3 is a horizontal section on the line 3Z- of Fig. l;

Fig. 4 is a vertical sectional elevation of a modified form of cupolafurnace apparatus; and K Fig. 5 is a horizontal section on the line 5-5of Fig. 4.

The same characters of reference indicate'the same parts throughout theseveral views.

One example of carrying out the inven tion is illustrated by theapparatus shown in Figs. 1, 2 and 3. This apparatus is in tended forpractising the invention in a cupola furnace having a fore-hearth.Referring to said Figs. 1, 2 and 3. the reference numeral ll representsa cupola constituted of a stack 12 in the upper part. the bosh 13 in theintermediate part. and the hearth 14. Below the bosh 13 and above thehearth It is a bustle pipe 15 which supplies preheated air to theinterior of the furnace through the series of twyers lb. The charge tobe treated in the furnace is introduced into the top of the stack 12 inthe usual way and, when in the furnace consists of a mixture of pigiron, or scrap or burnt iron, coke and a basic material such as limestone, for neutralizing the acidity of the ash and forming the slagwhich tloats or stratilics on the top of the molten metal in the bottomof the hearth.

In addition to its neutralizing action on the acidity of the ash, thelime stone slag stratum indicated by the reference nun'ieral 17 has anaffinity for sulfur and such property of the slag to absorb sulfur, andalso to promote deoxidiziug of the molten iron is augmented bv contactof incandes ent carbon. which dips into the slag stratum. The moltenmetal [lows in small drops, or

in the form of spray, downwardly through the solid portions of thecharge in the melting zone, and dropping through the slag stratum on topof the mass of molten metal in the bottom of the hearth, the small dropsof molten metal are subjected to the pro,- longed action of the slagwhich action is augmented by the submerged particles of incandescentcarbon. In its passage through the slag stratum, a reaction is effectedbetween the basic compounds present in the slag and the sulfur contentin the metallic iron causing sulfur to be absorbed from the iron andretained by the slag, with which the sulfur combines to form principallythe compound, calcium sulfid. The absorption of sulfur by the slag maybe represented, for example, by the following two equations:

CaO+O:CO|-Ca Ca-l-FeS CaS-Hie sulfid is soluble in and will be retainedby the slag. The importance of the presence of incandescent carbon isillustrated by the first formula given above, inasmuch as the action ofthe carbon is first to reduce the calcium oxid to metallic calcium,thereby augmenting the affinity of the slag stratum for absorption of.sulfur from the metal which passes through the slag. A further result ofthe contact of incandescent carbon with the slag stratum, is to promotedeoxidizing of the metal as it drips through the slag, inasmuch as theincandescent carbon has a very high affinity for oxygen. Suchincandescent carbon further promotes the reduction of manganese oxidspresent in the slag which originated in the iron charged in the cupola.There is thus effected a re juvenation of the iron, by restoring theretosuchessential elements as manganese and silicon, which elements arefrequently lost in ordinary remelting processes. Other elements are alsoreduced, such for example as iron contained in the coke, and this ironmay be recovered and added to the product of the remelting furnace.cupola practice, it frequently happens that the metal discharged fromthe cupola contains more sulfur and oxygen and less manganese andsilicon than that contained in the metal originally charged into thecupolzf, for the reason that, in the region of the twyers, the oxidizingeffect of the air is not counteracted by the reducing effect of a slagmass, as the slag is discharged from the furnace as soon as it isformed.

-The )rcsent invention b continuous] In ordinary H furnace, counteractsthis oxidizing tendency, and has the opposite effect of obtainin aroduct/havin less ox en and sulincorporate in the charge a largeproportion of rusty iron scrap of poor quality and to effect completerejuvenation, without resort to remelting in the blast furnace, asordinary practice always requires. The rejuvenation of scrap or oftenremelted iron of poor quality is thus accomplished di rectly in thecupola, and blast furnace treatment, for this purpose, is avoided.

In accordance with the invention, the

above described factors which augmentdesulfurization, deoxidation andrejuvenation of the iron are maintained continuously in their conditionof maximum effect, during operation of the remelting furnace. In orderto effect this result and to secure a maximum desulfurizing effectpromoted by the action of the slag and'immersed incandescent carbon, theinvention provides for .the maintenance of a continuous mass of slag inthe hearth of the remelting furnace as contra-distinguished fromordinary practice in which the slag and metal are discharged from thefurnace as soon as they form.' By the invention, amass ofsulfurabsorbing slag is maintained at all times within the'furnace,thereby producing a condition which results in maximum desulfurizationand promotes the obtaining of a product of uniformly low sulfur content.In fact the refined iron obtained, as a result of the practice of theinvention, contains appreciably less sulfur and also appreciably lessoxygen and more manganese than. is present in iron refined by presentprocesses, there being only small traces of sulfur present in therefined iron obtained by this invention. Accordingly, the invention may,if desired, be exploited for the purpose of producing refined ironhaving a specific maximum sulfur content, in which case it will bepossible to utilize in the remelting furnace coke having a greaterproportion of sulfur than could be used in present practice, to obtainrefined iron of the required specifications. Consequently, coke producedfrom many coals, which has been heretofore rejected for metallurgicalpurposes, is made available for such purposes.

One way of practising the invention is illustrated in Figs. 1, 2 and 3,and this consists in maintaining continuously during the operation ofthe furnace, constant levels respectively of the molten metal andsuperposed slag strata in the hearth of thefurnace. This is accomplishedby effecting withdrawal of the metal and slag separately from theirrespective strata, through over flow-ducts l8 and 19. The metaloverflowduct 18 extends upwardly from the hearth of the furnace at apoint below the level of the molten metal and thence downwardly to asealedu' 'essel 20. The slagoverfiow-duct 19 extends'from the hearth" ofthe furnace just below the level of the twyers 16 to the metaloverflow-duct 18,-through which the slag passes from the duct 19 to thevessel 20, from which it may be discharged separately from the metal.The/fixed slag overflow pipe 19 determines the height of the slag levelin the hearth of the furnace, whereas the fixed location of the crest ofthe metal overflowpipe 18 determines the height of the level of moltenmetal. In practice, the relation of these respective heights may beexpressed as follows: The height of the crest of the metal overflow pipeabove its junction point with the hearth of the furnace equals theheight of the molten metal in the furnace above said junction point plustwosevenths of the height of the slag stratum in the hearth of thefurnace, assuming that the specific gravity of the slag be two and thatof the iron be seven.

In this manner constant levels, both of slag and of molt en metaharemaintained in the hearth of the furnace and this condition is combinedwith continuous discharge both of slag and of the refined metal from thefurnace. Drawing off of the'slag and metal, as soon as they are formed,is el iminated,

. and conditions which insure a maxlmum ab-v sorption of sulfur from themetal are maintained uninterruptedly in the furnace, with the resultthat the product contains but aminimum. content of sulfur.

As shown in Figs. 1, 2 and 3, an open hearth furnace operation may bedirectly combined with the cupola operation, for further modifying thecomposition of the refined metal obtained from the cupola. Connectedwith the opposite ends of the fore-hearth oitub 21 are regenerators 22,said regenerators being alternately heated by the waste products fromthe hearth and giving up their heat to effect pre-heating of theairwhich enters the hearth to support combustion. The overflow-ductlt) isconnected with the opposite ends of the hearth by gas ducts 23 the flowthrough which is respectively controlled by valves 24;, therebypermitting the combustible gas from the cupola to be burned inconjunction with the air suppliedby either regenerator. In this way thecupola gas, of high calorific value, is lead directly into an openhearth furnace and there utilized for open hearth treatment of therefined metal discharged from the cupola.

In Figs. 4 and 5, there is illustrated an application of the inventionto a simple cupola furnare apparatus. The furnace illustrated in thesefigures is supported by pedestals 25 of any approved construction andconsists essentially of an outer cylindrical metallic shell 26surrounding an inner cylindrical refractory lining 27. The twyers 28 aredisposed in series around the furnace, and are connected at their outerends with an air inlet pipe 29 which encircles the furnace and suppliesthe air for supporting combustion within the furnace. Just below thetwyers and located inthe hearth 30 of the cupola is an overflow-duct 31for the slag. In the bottom of the hearth is a discharge duct 32 for themolten metal, such discharge duct 32 communicating at its outer end withan upwardly extending duct 33 through which the metal flows to and overan overflow-spout 34 which carries the refined metal to a closedreceiver 35. The receiver 35 is constructed of an outer metallic shell36 and an inner-refractory lining 37, and is provided with an inlet38and ,with an outlet 39 through which the refined metal may be dischargedas desired. The crest of the vertical duct 33 is related to the slag andmolten metal levels within the hearthof the furnace, in the same manneras the crest of the duct 18 utilized in the form of the inventionillustrated in Figs.

iron and its alloys, the continuous maintenance, in the hearth of acupola, of a pool of slag in the presence of incandescent carbon thathas sunk below the level of the air blast and into said slag pool,combined with the passage of the remelted ,iron through said slag poolto effect absorption of sulfur from the iron; substantially asspecified.

2. In the cupola remelting treatment of iron and its alloys, thecontinuous mainte nance, in the hearth of'a cupola, of a pool of slag inthe presence of incandescent carbon that has sunk below the level of theair blast and into said slag pool, combined with the passage of theremelted iron in the form of a spray through said slag pool to effectabsorption of sulfur from the iron; sub stantially as specified.

3. In the cupola remelting treatment of iron and its alloys, thecontinuous mainte nance, in the hearth of a cupola, of a pool of basicslag in the presence of incandescent carbon that has sunk below thelevel ofthc I in the presence of incandescent carbon that has sunk belowthe level of the air blast and into said slag stratum, combined with thepassage of the remelted iron through said slag stratum to effectabsorption of the sulfur from the iron; substantially as specified.

5. In the remelting of iron and its alloys with coke, the continuousmaintenance of a mass of basic slag at a constant level above the bottomof the incandescent coke to efiect (.lesulturization of the remeltedmetal during its passage through the slag and to maintain a reducingzone through which the remelted iron passes before being discharged,substantially as specified.

6. In the remelting of iron and its alloys with coke, the continuousmaintenance of a mass of basic slag above the bottom of the incandescentcoke to effect desulfurization of the remelted metal during its passagethrough the slag and to maintain a reducing zone through which theremelted iron passes -before being discharged, substantially asspecified.

7. A cupola furnace comprising: a remelting chamber, twyers, and meansfor controlling the molten metal in the hearth of said chamber insubstantial proportion to the difference in specific gravities of saidmetal and the superimposed sla to-maintain substantial masses of the moten metal and superimposed slag respectively at constant levels in thelower portion of said remelting chamber and below the level of the blastfrom the twyers; substantially as specified.

8. A cupola furnace comprising: a remelting chamber, twyers, a slagoverflow means below the level of the twyers, and a molten metaloverflow means below said slag overflow means, said overflow meanscontrolling the molten metal level in the hearth of said chamber insubstantial proportion to the difference in specific gravities of saidmetal and the superimposed slag and operating to maintain-constantlevels of substantial masses of the molten metal and superimposed slagin the hearth of said remelting'chamber below the level of the blastfrom the twyers; sub stantially as specified. 9. A cupola furnacecomprising: a re melting chamber, twyers, a slag overflow means belowthe level of the twyers, and an overflow means for the molten metalbelow said slag overflow means, said means. controlling the molten metallevel in the hearth of said chamber in substantial proportion to thedifference in specific gravities of said metal and superimposed slag;substantially as specified. I

10. In the remelting treatment of iron and its alloys; passing theremelted iron through a mass of slag in the presence of incandescentcarbon, to effect absorption of sulfur from the iron; withdrawing thedesulfurized iron and gas; and burning such gas in preheated blastandinto said slag the presence of the withdrawn. iron to eiiect furtherrefining of the iron; substantially,

as specified.

11. A cupola furnace, comprising: a remelting chamber; twyers; afore-hearth; means below the level of the twyers for per mitting gas topass into said fore-hearth; and a molten metal over-flow means alsoconnected with said fore-hearth; substantially as specified.

12. A cupola furnace, comprising: a remelting chamber; twyer's; afore-hearth; regenerators for supplying preheated. air to saidfore-hearth; means below the level of the twyers for permitting gas topass into said forehearth; and a molten metal overflow means alsoconnected with said forehearth; substantially as specified.

13. A cupola furnace comprising: a remelting chamber, twyers, and meansfor controlling the molten metal in the hearth of said chamber insubstantial proportion to the difference in specific gravities of saidmetal and the superimposed slag, to main tain continuously, in the lowerportion of said chamber and below the level of the blast from thetwyers, levels of substantial masses of the molten metal andsuperimposed slag; substantially as specified.

14. In the cupola treatment of iron and its alloys, a process consistingin desulfuriaing the iron and in reducing slag-compounds, or the natureof those derived from the iron, and in rejuvenating the iron with thealloy-- ing elements recovered from such compounds; substantially asspecified.

15. In the cupola treatment of iron and its alloys, a process consistingin desulfurizing and deoxidizing the iron, and in reducingslag-compounds and conserving in the iron the manganese and siliconrecovered from such compounds; substantially as specified.

16. In the cupola remelting treatment of iron and its alloys: a processwhich consists in subjecting the iron to the treatment of a blast ofpreheated air and in effecting a passage of the remelted iron through apool of slag in the presence of incandescent carbon that has sunk belowthe level of said.

pool; substantially as specified. I

17. A cupola furnace comprising: a remelting chamber, means forsupplying a blast of preheated air to said r'emelting chamber, and meansfor controlling the molten metal in the hearth of said chamber insubstantial proportion to the difference in specific gravities of saidmetal and superimposed slag, to maintain substantial masses of themolten metal and superimposed slag respectively at constant levels inthe lower portion of said remelting chamber and below the level of theblast from the twyers; substantially as specified.

HEINRICH KOPPERS.

